The colors of seawater, ranging from deep blue to emerald green, reflect a complex interplay of natural phenomena.

To comprehend why seawater appears in different hues in various locations, we must first understand the intrinsic color of water and how light behaves when it passes through it.

Contrary to common perception, pure water is blue. This may come as a surprise because the water we encounter daily appears colorless and transparent.

This apparent lack of color results from the small volumes we typically see, which are insufficient to reveal water's true color. If we were to fill a container the size of a building with pure water, we would observe its true blue hue.

The color of water primarily depends on the reflection and absorption of light by water molecules. White light, such as sunlight, comprises a spectrum of seven colors.

Within this spectrum, light in the red to green wavelength range is more easily absorbed by water molecules, whereas blue light is reflected. This selective absorption and reflection cause seawater to appear blue.

However, the color of seawater is not uniform. In the open ocean, far from the coast, seawater appears dark blue, sometimes even with a hint of purple.

Conversely, near the coastline, the color of seawater gradually transitions from blue to green and then to yellow-green. This variation is closely linked to the presence of plankton and the depth of the water.

Near the coastline, seawater is rich in organic matter and aquatic plants washed in from the land. Among these are tiny green plants known as phytoplankton, which contain chlorophyll.

Chlorophyll absorbs most of the red and blue light, reflecting green light instead. Consequently, the seawater near the coast appears green.

From space, the color of the ocean provides clues about the distribution of life on Earth. Green seas resemble tropical rainforests on land, teeming with vitality, while deep blue waters are akin to uninhabited deserts, with sparse life.

The absorption of light by seawater and its plankton also influences underwater colors. Imagine you are piloting a yellow submarine. Near the surface, the submarine remains yellow.

However, as it descends, the amount of light reaching the submarine diminishes. At a depth of 30 meters, sunlight's yellow, orange, and red wavelengths are almost entirely absorbed by water molecules, leaving only blue and green light.

Consequently, the submarine appears blue-green. If it descends further, to the point where even green light is absorbed, the submarine turns dark blue.

The concentration of plankton increases the water's turbidity and its light absorption. Thus, in turbid waters, the environment darkens more quickly as you descend.

In addition to phytoplankton, other microscopic particles, such as suspended sand and mud, can scatter and absorb light of various wavelengths, further altering seawater's color.

The depth of the water also significantly impacts its color. In shallow waters, sunlight can penetrate to the seabed, where sand, coral reefs, and seaweed reflect light, causing the water to appear light blue or green. In deep-sea regions, sunlight cannot reach the seabed, rendering the seawater dark blue or nearly black.

Meteorological conditions also affect the observed color of seawater. On sunny days, direct sunlight enhances the water's pure and deep hues. On cloudy or rainy days, clouds block sunlight, causing the seawater to appear duller and more gray-blue.

The color of seawater is the result of a complex interaction of factors, including the absorption and reflection of light, the distribution of plankton, water depth, and weather conditions. These factors collectively shape the vibrant and varied oceanic landscapes we observe, showcasing nature's intricate beauty and complexity.